The fracture toughness of the tempered martensitic stainless steel Eurofer97 has been experimentally characterized in the ductile-to-brittle transition (DBT) region with sub-sized compact tension specimens. The median fracture toughness–temperature curve in the lower transition region has been found to deviate somewhat from the master curve as described in the ASTM E1921-03 standard. Two-dimensional finite element simulations of the compact tension specimen have been performed. The analysis of the stress fields around the crack tip have been used to define a local criterion for cleavage based upon the attainment of a critical stress over a critical area. This local criterion has been used to reconstruct the lower bound in the transition region. The calibration procedure of the critical parameters has been discussed in detail as well as the uncertainty in the critical values. It is shown in particular that the critical stress is well defined while the model leads to a rather larger uncertainty in the determination of the critical area. © 2008 Elsevier Ltd. All rights reserved.